I like the Vltor because they have so many designs -- clubfoot and standard versions of collapsible, plus A1- and A2-length fixed stocks -- and you can swap them in seconds without changing the buffer tube.

As far as the buffer that comes with it...

Buffers to M16 owners are like shoes for Imelda Marcos: You can never own too many, because they are the simplest variable to tune your '16's ROF and reliability. My Vltor-supplied buffer is somewhere in the box of a dozen-plus buffers I currently use. I have a different fave buffer for each upper, but a range of two or three that work with each upper when I want to speed 'er up or slow 'er down.

I can't remember whether the spring I use is Colt or Vltor: They seem interchangable, with approximately the same milspec spring rate and function. About the only time I notice the spring is that in a few rare applications I switch to the Wolff Xtra Power recoil spring. The Wolff is too stiff IMHO for most applications, so generally I stick to milspec.

HTH!